ENH: add kwargs rename to Styler.format_index for overwriting index labels

doc/source/whatsnew/v1.5.0.rst

@@ -20,6 +20,8 @@ Styler
 ^^^^^^
 
   - New method :meth:`.Styler.to_string` for alternative customisable output methods (:issue:`44502`)
+  - New keyword argument ``rename`` added to :meth:`.Styler.format_index` to allow simple label string replacement (:issue:`45288`)
+  - Various bug fixes, see below.
   - Added the ability to render ``border`` and ``border-{side}`` CSS properties in Excel (:issue:`42276`)
   - Added a new method :meth:`.Styler.concat` which allows adding customised footer rows to visualise additional calculations on the data, e.g. totals and counts etc. (:issue:`43875`, :issue:`46186`)
   - :meth:`.Styler.highlight_null` now accepts ``color`` consistently with other builtin methods and deprecates ``null_color`` although this remains backwards compatible (:issue:`45907`)

pandas/io/formats/style_render.py

@@ -1168,6 +1168,7 @@ def format_index(
         thousands: str | None = None,
         escape: str | None = None,
         hyperlinks: str | None = None,
+        rename: list[str] | list[list[str]] | None = None,
     ) -> StylerRenderer:
         r"""
         Format the text display value of index labels or column headers.
@@ -1179,9 +1180,12 @@ def format_index(
         formatter : str, callable, dict or None
             Object to define how values are displayed. See notes.
         axis : {0, "index", 1, "columns"}
-            Whether to apply the formatter to the index or column headers.
+            Whether to apply the ``formatter`` or ``rename`` to the index or column
+            headers.
         level : int, str, list
-            The level(s) over which to apply the generic formatter.
+            The level(s) over which to apply the generic ``formatter``, or ``rename``.
+            In the case of ``rename`` defaults to the last level of a MultiIndex,
+            for the reason that the last level is never sparsified.
         na_rep : str, optional
             Representation for missing values.
             If ``na_rep`` is None, no special formatting is applied.
@@ -1203,6 +1207,17 @@ def format_index(
             Convert string patterns containing https://, http://, ftp:// or www. to
             HTML <a> tags as clickable URL hyperlinks if "html", or LaTeX \href
             commands if "latex".
+        rename : list of str, list of list of str
+            Values to replace the existing index or column headers. If specifying
+            more than one ``level`` then this should be a list containing sub-lists for
+            each identified level, in the respective order.
+            Cannot be used simultaneously with ``formatter`` and the associated
+            arguments; ``thousands``, ``decimal``, ``escape``, ``hyperlinks``,
+            ``na_rep`` and ``precision``.
+            This list (or each sub-list) must be of length equal to the number of
+            visible columns, see examples.
+
+            .. versionadded:: 1.5.0
 
         Returns
         -------
@@ -1238,6 +1253,10 @@ def format_index(
         When using a ``formatter`` string the dtypes must be compatible, otherwise a
         `ValueError` will be raised.
 
+        Since it is not possible to apply a generic function which will return an
+        arbitrary set of column aliases, the argument ``rename`` provides the
+        ability to automate this, across individual index levels if necessary.
+
         .. warning::
            `Styler.format_index` is ignored when using the output format
            `Styler.to_excel`, since Excel and Python have inherrently different
@@ -1298,50 +1317,117 @@ def format_index(
         {} & {\textbf{123}} & {\textbf{\textasciitilde }} & {\textbf{\$\%\#}} \\
         0 & 1 & 2 & 3 \\
         \end{tabular}
+
+        Using ``rename`` to overwrite column names.
+
+        >>> df = pd.DataFrame([[1, 2, 3]], columns=[1, 2, 3])
+        >>> df.style.format_index(axis=1, rename=["A", "B", "C"])  # doctest: +SKIP
+                A      B       C
+        0       1      2       3
+
+        Using ``rename`` to overwrite column names of remaining **visible** items.
+
+        >>> df = pd.DataFrame([[1, 2, 3]],
+        ...                   columns=pd.MultiIndex.from_product([[1, 2, 3], ["X"]]))
+        >>> styler = df.style  # doctest: +SKIP
+                1      2       3
+                X      X       X
+        0       1      2       3
+
+        >>> styler.hide([2], axis=1)      # hides a column as a `subset` hide
+        ...       .hide(level=1, axis=1)  # hides the entire axis level
+        ...       .format_index(axis=1, rename=["A", "C"], level=0)  # doctest: +SKIP
+                A      C
+        0       1      3
         """
         axis = self.data._get_axis_number(axis)
         if axis == 0:
             display_funcs_, obj = self._display_funcs_index, self.index
+            hidden_labels = self.hidden_rows
         else:
             display_funcs_, obj = self._display_funcs_columns, self.columns
+            hidden_labels = self.hidden_columns
         levels_ = refactor_levels(level, obj)
 
-        if all(
+        formatting_args_unset = all(
             (
                 formatter is None,
-                level is None,
                 precision is None,
                 decimal == ".",
                 thousands is None,
                 na_rep is None,
                 escape is None,
                 hyperlinks is None,
             )
-        ):
+        )
+
+        if formatting_args_unset and level is None and rename is None:
+            # clear the formatter / revert to default and avoid looping
             display_funcs_.clear()
-            return self  # clear the formatter / revert to default and avoid looping
 
-        if not isinstance(formatter, dict):
-            formatter = {level: formatter for level in levels_}
-        else:
-            formatter = {
-                obj._get_level_number(level): formatter_
-                for level, formatter_ in formatter.items()
-            }
+        elif rename is not None:  # then apply a formatting function from arg: rename
+            if not formatting_args_unset:
+                raise ValueError(
+                    "``rename`` cannot be supplied together with any of "
+                    "``formatter``, ``precision``, ``decimal``, ``na_rep``, "
+                    "``escape``, or ``hyperlinks``."
+                )
+            else:
+                visible_len = len(obj) - len(set(hidden_labels))
+                if level is None:
+                    levels_ = [obj.nlevels - 1]  # default to last level
+                elif len(levels_) > 1 and len(rename) != len(levels_):
+                    raise ValueError(
+                        f"``level`` specifies {len(levels_)} levels but the length of "
+                        f"``rename``, {len(rename)}, does not match."
+                    )
 
-        for lvl in levels_:
-            format_func = _maybe_wrap_formatter(
-                formatter.get(lvl),
-                na_rep=na_rep,
-                precision=precision,
-                decimal=decimal,
-                thousands=thousands,
-                escape=escape,
-                hyperlinks=hyperlinks,
-            )
+                def alias_(x, value):
+                    return value
+
+                for i, lvl in enumerate(levels_):
+                    level_alias = rename[i] if len(levels_) > 1 else rename
+                    if len(level_alias) != visible_len:
+                        raise ValueError(
+                            "``rename`` must be of length equal to the number of "
+                            "visible labels along ``axis``. If ``level`` is given and "
+                            "contains more than one level ``rename`` should be a "
+                            "list of lists with each sub-list having length equal to"
+                            "the number of visible labels along ``axis``."
+                        )
+                    for ai, idx in enumerate(
+                        [
+                            (i, lvl) if axis == 0 else (lvl, i)
+                            for i in range(len(obj))
+                            if i not in hidden_labels
+                        ]
+                    ):
+                        display_funcs_[idx] = partial(alias_, value=level_alias[ai])
+
+        else:  # then apply a formatting function from arg: formatter
+            if not isinstance(formatter, dict):
+                formatter = {level: formatter for level in levels_}
+            else:
+                formatter = {
+                    obj._get_level_number(level): formatter_
+                    for level, formatter_ in formatter.items()
+                }
+
+            for lvl in levels_:
+                format_func = _maybe_wrap_formatter(
+                    formatter.get(lvl),
+                    na_rep=na_rep,
+                    precision=precision,
+                    decimal=decimal,
+                    thousands=thousands,
+                    escape=escape,
+                    hyperlinks=hyperlinks,
+                )
 
-            for idx in [(i, lvl) if axis == 0 else (lvl, i) for i in range(len(obj))]:
-                display_funcs_[idx] = format_func
+                for idx in [
+                    (i, lvl) if axis == 0 else (lvl, i) for i in range(len(obj))
+                ]:
+                    display_funcs_[idx] = format_func
 
         return self
 

pandas/tests/io/formats/style/test_format.py

@@ -434,3 +434,82 @@ def test_1level_multiindex():
     assert ctx["body"][0][0]["is_visible"] is True
     assert ctx["body"][1][0]["display_value"] == "2"
     assert ctx["body"][1][0]["is_visible"] is True
+
+
+def test_basic_rename(styler):
+    styler.format_index(axis=1, rename=["alias1", "alias2"])
+    ctx = styler._translate(True, True)
+    assert ctx["head"][0][1]["value"] == "A"
+    assert ctx["head"][0][1]["display_value"] == "alias1"  # alias
+    assert ctx["head"][0][2]["value"] == "B"
+    assert ctx["head"][0][2]["display_value"] == "alias2"  # alias
+
+
+def test_basic_rename_hidden_column(styler):
+    styler.hide(subset="A", axis=1)
+    styler.format_index(axis=1, rename=["alias2"])
+    ctx = styler._translate(True, True)
+    assert ctx["head"][0][1]["value"] == "A"
+    assert ctx["head"][0][1]["display_value"] == "A"  # no alias for hidden
+    assert ctx["head"][0][2]["value"] == "B"
+    assert ctx["head"][0][2]["display_value"] == "alias2"  # alias
+
+
+@pytest.mark.parametrize("level", [None, 0, 1])
+def test_rename_single_levels(df, level):
+    df.columns = MultiIndex.from_tuples([("X", "A"), ("Y", "B")])
+    styler = Styler(df, cell_ids=False, uuid_len=0)
+    styler.format_index(axis=1, level=level, rename=["alias1", "alias2"])
+    ctx = styler._translate(True, True)
+    assert len(ctx["head"]) == 2  # MultiIndex levels
+
+    level = 1 if level is None else level  # defaults to last
+    assert f"level{level}" in ctx["head"][level][1]["class"]
+    assert ctx["head"][level][1]["display_value"] == "alias1"
+    assert ctx["head"][level][2]["display_value"] == "alias2"
+
+
+@pytest.mark.parametrize("level", [[0, 1], [1, 0]])
+def test_rename_multi_levels_order(df, level):
+    df.columns = MultiIndex.from_tuples([("X", "A"), ("Y", "B")])
+    styler = Styler(df, cell_ids=False, uuid_len=0)
+    styler.format_index(axis=1, level=level, rename=[["a1", "a2"], ["b1", "b2"]])
+    ctx = styler._translate(True, True)
+
+    assert ctx["head"][1 - level[1]][1]["display_value"] == "a1"
+    assert ctx["head"][1 - level[1]][2]["display_value"] == "a2"
+    assert ctx["head"][1 - level[0]][1]["display_value"] == "b1"
+    assert ctx["head"][1 - level[0]][2]["display_value"] == "b2"
+
+
+@pytest.mark.parametrize(
+    "level, rename",
+    [
+        ([0, 1], ["alias1", "alias2"]),  # no sublists
+        ([0], ["alias1"]),  # too short
+        (None, ["alias1", "alias2", "alias3"]),  # too long
+        ([0, 1], [["alias1", "alias2"], ["alias1"]]),  # sublist too short
+        ([0, 1], [["a1", "a2"], ["a1", "a2", "a3"]]),  # sublist too long
+    ],
+)
+def test_rename_warning(df, level, rename):
+    df.columns = MultiIndex.from_tuples([("X", "A"), ("Y", "B")])
+    styler = Styler(df, cell_ids=False, uuid_len=0)
+    msg = "``rename`` must be of length equal to"
+    with pytest.raises(ValueError, match=msg):
+        styler.format_index(axis=1, level=level, rename=rename)
+
+
+@pytest.mark.parametrize(
+    "level, rename",
+    [
+        ([0, 1], [["a1", "a2"]]),  # too few sublists
+        ([0, 1], [["a1", "a2"], ["a1", "a2"], ["a1", "a2"]]),  # too many sublists
+    ],
+)
+def test_rename_warning2(df, level, rename):
+    df.columns = MultiIndex.from_tuples([("X", "A"), ("Y", "B")])
+    styler = Styler(df, cell_ids=False, uuid_len=0)
+    msg = "``level`` specifies 2 levels but the length of"
+    with pytest.raises(ValueError, match=msg):
+        styler.format_index(axis=1, level=level, rename=rename)